A ventilator, by means of which a patient is mechanically ventilated, can be actuated with such a method, and a control signal, which switches the ventilator between a phase of inhalation, during which breathing air is fed to the patient, and a phase of exhalation, during which the patient exhales, is generated from the measured signal, which is obtained at the patient. When the patient is making efforts, albeit insufficiently, on his own to inhale and when he fails to exhale are determined from the measured signal.
It is already known in this connection from the state of the art that flow sensors can be used, which detect the volume flow in a tube section between the ventilator and the patient, and the ventilator will then be switched into the phase of inhalation or the phase of exhalation depending on the direction and the value of this volume flow.
Such a procedure is, however, disadvantageous, because it is necessary for a switch-over that the patient must have made a comparatively great effort to bring about a measurable change in the volume flow, and this effort will then cause the ventilator to be switched over. Another drawback is that the switch-over takes place only when the patient has already made efforts and was not supporting the breathing at an earlier point time already.
It is desirable against the background to use another physiological signal, which is markedly more sensitive to the start of the breathing efforts than a volume flow signal, instead of the volume flow signal for controlling the ventilator.
It is already known in this connection from the state of the art, for example, EP 1 056 499 B1 or U.S. Pat. No. 4,915,103, that the electromyogram signal can be used, but the problem arises here that the signal detected with electrodes on the body surface or, as is disclosed in EP 1 056 499 B1, with an electrode in the trachea, has a considerable interference component. In addition, the potentials, which are detected in the process and with which muscles that are relevant for breathing are stimulated, are very low. Especially compared to the cardiac signals (EKG signals), these signals are lower by several orders of magnitude, so that the cardiac signals represent major artifacts.
Great efforts are therefore needed to detect in the electromyogram signal the transition between a phase, during which no efforts are being made by the patient and which reflects the phase of exhalation and a phase of inhalation, during which the muscles relevant for breathing are stimulated. However, the electromyogram signal, which is sensitive to a change in the stimulation potentials for the muscles relevant for breathing, offers the great advantage that the start of the breathing efforts can be detected with this signal very well.
However, the state of the art fails to offer any reliable methods with which a distinction can be made between the phase of inhalation and the phase of exhalation in an electromyogram signal recorded in the area of the muscles relevant for breathing and on the basis of which a ventilator can be actuated.